The present invention relates to an engine valve performance controller, and more particularly, to an improvement in control for preventing knocking.
In recent years, various technologies have been put into practice to improve engine performance. The valve performance of engine valves (intake and exhaust valves) characteristics such as valve timing or valve lift are varied to reduce trade-off under different operational conditions (for example, refer to Japanese Patent Laid-Open Publication No. 2001-263015).
Under severe operational conditions involving high temperatures and high loads, the compression end temperature within a combustion chamber becomes high. In such a state, knocking has a tendency to occur. In such a case, the ignition timing is normally retarded to decrease the combustion speed and thus prevent knocking.
However, if the combustion speed is decreased by retarding the ignition timing, the exhaust gas temperature will rise. Therefore, if the ignition timing is significantly retarded, the fuel injection amount must be increased to prevent the temperature of an exhaust gas purifying catalyst from becoming excessively high. Accordingly, when knocking is prevented just by retarding the ignition timing, this would lower fuel efficiency due to the increase of the fuel injection amount.
Accordingly, it is an object of the invention to provide an engine valve performance controller that efficiently prevents knocking.